The present paper deals with the ecological studies of Alisagar lake of Nizamabad District, Telangana. The water samples were collected for a period of 2 years (June-2014 to May-2016) to assess the quality of water. The lake water was alkaline throughout the period of investigation. High concentration of dissolved oxygen, carbonates and low concentration of chlorides, bicarbonates, total hardness and organic matter were recorded throughout the period of investigation. Four groups of phytoplankton were recorded. in the lake. Among the four groups Diatoms were dominant and showed rich diversity followed by Chlorophyceae. Low temperature, high dissolved oxygen and silica favored the growth of diatoms. The maximum growth of diatoms was recorded during winter and minimum during summer and rainy season. Temperature, bicarbonates, nitrates, phosphates and organic matter were exhibiting direct relationship with Chlorophyceae.